map::slippy::cache - Mapping utilities

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# map::slippy::cache(n) 0.2 tcllib "Mapping utilities"

## Name

map::slippy::cache - Management of a tile cache in the local filesystem

## Synopsis

- package require Tcl 8.4
- package require Tk 8.4
- package require img::png
- package require map::slippy
- package require map::slippy::cache ?0.2?

- ::map::slippy::cache cacheName cachedir provider
- cacheName valid tile ?msgvar?
- cacheName exists tile
- cacheName get tile donecmd

## Description

This package provides a class for managing a cache of tiles for slippy-based maps in the local filesystem.

## API

::map::slippy::cache cacheName cachedir provider

  Creates the cache cacheName and configures it with both the path to the directory contaiing the locally cached tiles (cachedir), and the command prefix from which it will pull tiles asked for and not yet known to the cache itself (provider).

  The result of the command is cacheName.

### Methods

cacheName valid tile ?msgvar?

  This method checks the validity of a the given tile identifier. This is a convenience wrapper to ::map::slippy tile valid and has the same interface.

cacheName exists tile

  This methods tests whether the cache contains the specified tile or not. The result is a boolean value, true if the tile is known, and false otherwise. The tile is identified by a list containing three elements, zoom level, row, and column number, in this order.

cacheName get tile donecmd

  This is the main method of the cache, retrieving the image for the specified tile from the cache. The tile identifier is a list containing three elements, the zoom level, row, and column number of the tile, in this order.

  The command refix donecmd will be invoked when the cache either knows the image for the tile or that no image will forthcoming. It will be invoked with either 2 or 3 arguments, i.e.

  1. The string set, the tile, and the image.

  2. The string unset, and the tile.

  These two possibilities are used to either signal the image for the tile, or that the tile has no image defined for it.

  When the cache has no information about the tile it will invoke the provider command prefix specified during its construction, adding three arguments: The string get, the tile, and a callback into the cache. The latter will be invoked by the provider to either transfer the image to the cache, or signal that the tile has no image.

  When multiple requests for the same tile are made only one request will be issued to the provider.

## References

1. http://wiki.openstreetmap.org/wiki/Main_Page

## Keywords

cache, filesystem, location, map, slippy, tile, zoom